Method and apparatus for chromatographic moisture analysis



R. F. MARSH Nov. 28, 1967 METHOD AND APPARATUS FOR CHROMATOGRAPHICMOISTURE ANALYSIS Filed Aug. 10, 1964 QEQQEQ United States Patent3,355,367 METH'JD AND APPARATUS FOR CHROMATO- GRAPHKQ MOISTURE ANALYSISRoger F. Marsh, Arcadia, (Zalifi, assignor to ConsolidatedElectrodynamics Corporation, Pasadena, Calif., a corporation ofilaiifornia Filed Aug. 1'9, 1964, Ser. No. 388,624 6 (Iiaims. (Cl.204-1) This invention relates to apparatus for determining the presenceof water in non-aqueous fluids and in particular to a laboratoryapparatus including a chromatographic column and electrolytic celldetector for measuring the amount of water present in liquidhydrocarbons.

The analysis of gases and liquids has recently been improved by thedevelopment of electrolytic moisture cells such as described in UnitedStates Patents 2,816,067 to F. A. Keidel on Sept. 19, 1957; 2,830,945 toF. A. Keidel on Apr. 15, 1958; 2,994,853 to C. E. Berry on July 25,1-961 and 3,072,556 to Michael Czuha, Jr., on J an. 8, 1963.

However, electrolytic moisture cells are not readily utilizable for thedetection of water in certain non-aqueous fluids because the hygroscopicmaterial with which the electrodes of the cell are coated react with orcatalyze a reaction in these fluids. When this happens deposits, as forexample, polymers, due to the presence of a hydrocarbon component in thesample are formed which build up to foul and clog the capillary sizedtubing of the electrolysis cell and quickly render the cell useless.

The problem then is to provide an apparatus that will accept non-aqueousliquids such as hydrocarbons but will separate the water from thehydrocarbons prior to introduction to the electrolysis cell. The presentinvention accomplishes this by providing a packed chromatographic columnto which a sample of fluid to be analyzed is communicated, wherein aninert carrier is substituted for the nonaqueous fluid. An electrolyticcell having a pair of spaced apart electrodes bridged by a film ofhygroscopic material communicates with the output of the column andmeans for selectively flowing the water-inert carrier com.-

bination from the column to the cell are provided. Connected to thespaced apart electrodes are means for impressing a potential across themwhereby the Water presented to the cell and absorbed by the hygroscopicmaterial is electrolyzed. The electrolysis current is then metered todetermine the total amount of moisture present.

The chromatographic column used in conjunction with this invention is aconventional column used in gas chro matography. More specifically, thecolumn is a partition chromatograph in which analysis is accomplished bytransporting the water-carrying non-aqueous fluid to be analyzed to thechromatograph and substituting therein an inert carrier gas for thenon-aqueous fluid. 'A typical electrolytic cell utilized with thisinvention, comprises a pair of spaced bifilar wire coils, the coilsbeing supported against the inside wall of an enclosing tube or housing.A film of a desiccant or hygroscopic material, such as phosphorouspentoxide, is deposited on the coils and housing interior toelectrically bridge the spaces between adjacent turns of the two wirehelices.

A suitable voltage is applied to the two electrode coils, and when thehygroscopic material is conductive, say upon absorption of moisture, anelectrolytic path exists between the alternately spaced turns of thecoils. In operation therefore, as moisture is absorbed by thehygroscopic material from a gas stream flowing past the coils, thehygroscopic material becomes conductive, current flows between the coilsin the regions of conductivity and the water is electrolyzed to hydrogenand oxygen. The

electric current that flows, is an accurate measure of the rate ofmoisture absorption in accordance with Faradays law.

In a typical analysis than involving the use of apparatus according tothis invention a moisture bearing sample of hydrocarbons is introducedto a chamber where the sample is heated to a suflicient temperature toflash vaporize all components present. A carrier gas introduced into thechamber transports the vaporized sample to the chromatographic columnwhere the hydrocarbons are separated from the water and the carrier gassubstituted therefor. The water-carrier gas combination is then issuedfirst from the column and conveyed to the electrolytic detector wherethe water is absorbed by hygroscopic material m the cell andelectrolyzed by means of a source of potential connected to theelectrodes of the cell. The amount of current necessary to completelyelectrolyze the Water is integrated by an instrument included in thepotential supplying circuit to indicate the total amount of moisturepresent. The column is then back-flushed to remove the hydrocarbonswhich have been retained therein.

Such an apparatus is useful in providing a rapid, accurate analysis interms of weight of the water content of a liquid hydrocarbon regardlessof sample size. Given the total weight of the sample, simplecalculations transform this reading into percentages or parts permillion of water.

Typical cycle durations, from sample injection to completion ofback-flush are approximately fifteen minutes. Disadvantages due to thenecessity of establishing equilibrium conditions and providing largesample quantities characteristic of process instruments are avoidedsince the apparatus is capable of accurately analyzing samples of /2 cc.in volume or less and is restored to essentially its original conditionat the completion of each analysis.

These and other details of the apparatus and the operation of theprocess in accordance with this invention will be made clear byreference to:

FIG. 1 which depicts in schematic form the components of the apparatusof this invention, and FIG. 2, a graph of the variation of currentflowing in the cell during analysis of a typical sample.

In the schematic in FIG. 1 a sample of hydrocarbons to be analyzed isinjected in a vaporizer chamber 18 by means of a syringe 2 or similardevice. A source 4 of carrier gas is connected through a gas flowregulator 20 to the vaporizer chamber 18. The carrier gas is normally aninert gas such as nitrogen to which a predetermined amount of moisture,on the order of parts per million, has been added. It has been foundthat pre-wetting of the gas is necessary in order to prevent errors inthe operation of the analyzer. The system is calibrated to take intoaccount the predetermined amount of moisture added. The vaporizerchamber 18 is a heated chamber which is operated at approximately atemperature of C. This is accomplished by such means as an inductioncoil 6 connected to a source of potential 8 through a variablepotentiometer 10. At this temperature all components present in thesample to be analyzed are fiash vaporized when the sample is injectedinto the chamber. In addition, the carrier gas flowing into thevaporizer chamber also acts to strip the moisture from the vaporizedsample. The sample is then transported by the carrier gas through line22 into the chromatographic column 24.

The column 24 is a conventional gas-liquid partition chromatograph whichhas been provided with packing such that it is significantly retentiveof all components present in the sample except water. For example, onetype of packing or substrate to be used within the column is a supportof polytetraflucrethylene particles (powdered Teflon) as the solid phaseimpregnated with an oil or grease such as a #500 silicone oil as theliquid phase.

The packing just illustrated is merely one example of the combination ofliquid phase and solid support which can be used in the column. Otherpossibilities as the substrate include a polychlorine product marketedas Kel-F, which has a paraflin superimposed on it as the liquid phase.

As indicated, the important consideration is that the partitioningmaterial in the chromatograph be selected of introducing possiblecontaminants.

The separated Water vapor is carried over line 26 to the electrolyticcell 28. The electrolytic cell or hygrometer 28 is essentially a pair ofbifilar helical electrodes 25 and 27 disposed in a cell with theinterelectrode space being covered or bridged by means of a hygroscopicmaterial 29 such as phosphorous pentoxide. It is a characteristic ofsuch a cell that when water vapor is passed through it the vapor issorbed by the hygroscopic material. When water is sorbed by thismaterial a potential such as supplied by source 39 connected to theelectrodes 25 and 27 and completing the circuit causes a current to beconducted through the material 29. This current is conducted so long asmoisture is present in the phosphorous pentoxide. As the current isconducted'through the hygroscopic material the moisture present iselectrolyzed into hydrogen and oxygen and vented by suitable means. Atthe same time that the water is being electrolyzed the electrolyte isbein constantly regenerated in the cell so that when current ceases tohow the cell remains in its original condition ready to receive the nextsample.

Like the vaporizer chamber, the electrolytic cell 28 is also operated atan elevated temperature, approximately 50 to 70 C. This is done in orderto maintain the moisture carried into the cell 28 in the vapor phase.Liquids of any type entering the cell tend to dissolve the hygroscopicmaterial disposed therein and if allowed to persist ultimately renderthe cell inactive. The temperature of 50 to 70 is chosen because this ishigh enough to maintain the moisture in the vapor phase while at thesame time not exceeding the vapor pressure of the electrolyte, in thiscase, the phosphorous pentoxide.

The amount of current flowing in the cell is proportional to the amountof moisture present. If the current flowing in the cell were plottedagainst time a curve similar to the curve 33 shown in FIG. 2 is theresult. As shown in that figure the current at time, t begins to flow inthe cell, builds up to a maximum 34 indicated at t; and then diminishesto zero again at a time, t The area under the curve 33 is proportionalto the total amount of moisture present in the sample. By themathematical operation of integrating the area under the curve the totalamount of moisture present in the sample can be determined. A currentintegrating device 32 to perform this operation is connected in thecircuit with the source of potential 30. The integrating device 32 maybe any of the conventional mechanical or electrical devices which 7 arewell known in the art. Readout is normally in terms of the totalquantity of sample present. The carrier gas and hydrogen and oxygenliberated in the electrolysis cell are expelled through outlet 36.

After the current in the electrolytic cell has diminished to zeroindicating that the'moisture present has been completely electrolyzedthe flow of carrier gas is reversed by means of valve 14 and isredirected through line 38 into the outlet of the chromatograph 2.4. Bythis means the other sample components, most of which are stillcollected in the column, are back-flushed from the chromatograph andeliminated through auxiliary outlet 40. The analyzer is then ready forthe next analysis.

The analyzer is also useful in measuring the water content of certaingases such as ammonia and gaseous amines. In the same manner as liquidanalysis, injection of a known weight of sample under referencetemperature, pressure and volume conditions into the analyzer results inan output in terms of the total weight of water present in the sample.In addition to use as a batch orv laboratory analyzer it is alsopossible to adapt the analyzer of this invention to processapplications. Operation of the analyzer would still be on adiscontinuous, batch type basis with the apparatus being connected to :aprocess stream and provided With the capability of periodicallyextracting suitable samples. In this adaptation the orderiof the columnand vented and thereafter the water and inert.

carrier are transported to the electrolysis cell for Water contentmeasurement. a

What has been provided-is a laboratory-type analyzer for determining thetotal amount of moisture present in non-aqueous fluids such as ammoniaand hydrocarbons. Such a device is especially useful in liquid polymeranalysis applications Where itis possible to obtain the quick, accurateindications of an electrolytic detector while at the same timeprotecting the hygroscopic material of the detector from polymerformation. Since the amount of the sample is controllable, problems ofoverloading of the electrolytic cell are avoided simply by adjusting thesize of the sample taken Control of sample size also means that it ispossible to operate this instrument over Wide water content ranges, froma lower limit of parts per million of water to small percentages, i.e.,parts per hundred, of water as the upper limit. a

I claim: 1. Apparatus for determining the amount of Water present in anon-aqueous fluid sample, comprising:

a partition chromatograph having a column packed with a liquid solventdisposed on a solid support, the solvent and solid support beingselected such that water has the lowest adsor-bability therein of thecomponents in the fluid sample, means comprising a source of inertcarrier gas to which a predetermined amount of moisture has been'addedfor eluting the sample through'the column, an electrolytic cell having apair of spaced apart electrodes, a. body of hygroscopic materialinterconnecting the electrodes, means for selectively communicating thewater eluted from the column through the cell for absorption by thehygroscopicmaterial, and 7 means coupled to the cell for impressing apotential across the cell electrodes for electrolysis of the waterabsorbed by the hygroscopic material, the electrolysis current flowbetween the electrodes through the hygroscopic material being related tothe quantity of moisture electrolyzed in the cell.

2. An apparatus according to claim 1 wherein the solid support andliquid solvent packed in the column are Teflon particles and a siliconeoil respectively. I

3. A process for determining the amount of water present in liquidhydrocarbons comprising the steps of:

vaporizing a sample of the Water-bearing liquid hydrocarbons,

passing the vaporized sample with an inert carrier gas which has beenpre-wetted with a predetermined amount of moisture to a suitablechromatographic column, and substituting the inert carrier gas forhydrocarbons by passing the sample therethrough,

selectively flowing the water and inert carrier gas from the column toan electrolytic cell having a pair of electrodes bridged by a film ofhygroscopic material inten'orly of the cell, and

impressing an electric potential across the cell electrodes toelectrolyze moisture absorbed by the hygroscopic material.

4. A process according to claim 3 including the steps of integrating theelectrolysis current to indicate the total amount of moisture absorbedand back-flushing the chomatographic column to remove the hydrocarbonsretained therein.

5. A process for determining the amount of water present in fluidhydrocarbons comprising the steps of introducing a hydrocarbon samplewith an inert carrier gas which has been pre-wetted with a predeterminedamount of moisture to a suitable chromatographic column, andsubstituting the inert carrier gas for hydrocarbons by passing thesample therethrough, selectively flowing the water and inert carrier gasfrom the column to an elec trolytic cell having a pair of electrodesbridged by a film of hydroscopic material interiorly of the cell, andimpressing an electric potential across the cell electrodes toelectrolyze moisture absorbed by the hygroscopic material.

6. A process according to claim 5 including the steps UNITED STATESPATENTS 2,934,693 4/1960 Reinecke et al. 204195 3,169,832 2/1965Galloway et al. 23--232 3,257,609 6/1966 Sanford et al. 324-30 JOHN H.MACK, Primary Examiner. T. TUNG, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,355,367 November 28, 1967 Roger F. Marsh that error appears in theabove numbered pat- It is hereby certified nd that the said LettersPatent should read as ent requiring correction a corrected below.

Column 1, line 19, for "2,994,853" read 2,993,853 column 2, line 54,after "induction" insert heating Signed and sealed this 7th day ofJanuary 1969.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

3. A PROCESS FOR DETERMINING THE AMOUNT OF WATER PRESENT IN LIQUIDHYDROCARBONS COMPRISING THE STEPS OF: VAPORIZING A SAMPLE OF THEWATER-BEARING LIQUID HYDROCARBONS, PASSING THE VAPORIZED SAMPLE WITH ANINERT CARRIER GAS WHICH HAS BEEN PRE-WETTED WITH A PREDETERMINED AMOUNTOF MOISTRUE TO A SUITABLE CHROMATOGRAPHIC COLUMN, AND SUBSTITUTING THEINERT CARRIER GAS FOR HYDROCARBONS BY PASSING THE SAMPLE THERETHROUGH,SELECTIVELY FLOWING THE WATER AND INERT CARRIER GAS FROM THE COLUMN TOAN ELECTROLYTIC CELL HASING A PAIR OF ELECTRODES BRIDGED BY A FILM OFHYGROSCOPIC MATERIAL INTERIORLY OF THE CELL, AND IMPRESSING AN ELECTRICPOTENTIAL ACROSS THE CELL ELECTRODES TO ELECTROLYZE MOISTURE ABSORBED BYTHE HYGROSCOPIC MATERIAL.